Field of the Invention
This invention relates to a hydrostatic hybrid drive device for a hybrid drive train of a vehicle with a drive motor and a consumer driven by the drive motor.
Description of Related Art
Vehicles, for example motor vehicles or public transit vehicles, for example buses, preferably for urban mass transit, as well as mobile self-propelled machines, in particular industrial trucks, agricultural machines, forestry machines and construction machines such as excavators, wheel and telescoping loaders, tractors, combine harvesters, forage harvesters, sugar beet and potato harvesters, for example, have a drive train with a drive motor which is generally in the form of an internal combustion engine and which drives a consumer, which can be, for example, a traction drive of the vehicle.
Hybrid drive train concepts are being employed with increasing frequency on such vehicles. With regard to the construction of the hybrid drive train, known models include serial hybrid, parallel hybrid, or power-split hybrid drives.
Vehicles with a hybrid drive train are driven by a combination of different energy sources. In addition to the drive motor, which is generally in the form of an internal combustion engine, another energy source of the hybrid drive device is provided and carried onboard the vehicle. On a mechanical hybrid drive device, the other energy source can be formed, for example, by a flywheel; on an electrical hybrid drive device the other energy source can be formed by a battery, storage battery, or high-power capacitors; or on a hydrostatic hybrid drive device the other energy source can be formed by a hydrostatic accumulator.
Known hybrid drive devices have a high degree of system complexity and therefore entail a high level of capital investment, design, and production costs.
Known electric hybrid drive devices consist of an electrical energy storage device and an electrical machine that can be operated as a motor and a generator, which is generally in the form of an asynchronous machine and the actuation of which requires power electronics. For the electrical energy storage device or system, an automatic climate control system is also generally necessary to be able to heat and cool the electrical energy storage device or system in operation. Electrical hybrid drive devices are very cost-intensive on account of the low capacity of the electrical energy storage device or system and the additional components that are required for their operation from the fields of power electronics and climate control technology. In addition, the low power density and low energy density of the electrical energy storage device or system has a negative effect on the total weight of the, vehicle. A further disadvantage of electrical hybrid drive devices is that the electrical energy storage device or system represents an increased hazard potential, for example by self-ignition, as well as a danger to a person extinguishing a burning vehicle that has an onboard electrical energy storage device or system.
Known mechanical hybrid drive devices with a mechanical energy accumulator, such as a flywheel accumulator, generally work with very large or very fast rotating flywheels. However, the additional mass of the flywheel accumulator of a mechanical hybrid drive device results in a reduction of the energy consumption advantage of the vehicle because more energy is required for the acceleration of the vehicle in the traction cycles.
Known hydrostatic hybrid drive devices frequently require a large number of valves to temporarily store power in a hydrostatic accumulator and discharge it again. WO 2007/071362 A1 describes a generic hydrostatic hybrid drive device for a vehicle in which the hydrostatic hybrid drive device is in the form of a displacement machine which is connected on one side by means of a line with the tank and on the second side by means of an additional line with a hydrostatic accumulator. The displacement machine can be operated as a pump and as a motor and is provided for the delivery of hydraulic fluid in both directions of flow. The displacement machine is in the form of a controllable drive unit with a variable displacement volume. In WO 2007/071362 A1, different directions of flow of the displacement machine result during pump operation and motor operation. To make possible pump and motor operation in the same direction of rotation of the hydrostatic displacement machine, it must be possible to vary the drive unit in both directions and, therefore, it must be controllable in both directions from the position where the displacement volume is zero, as a result of which the control device of the hydrostatic displacement machine and thus the hydrostatic displacement machine of the hydrostatic hybrid drive device is correspondingly complex and expensive.